1. Field of Invention
The present invention relates to integrated circuit packaging.
2. Related Art
Semiconductor die or chip packages are used to protect the semiconductor device (e.g., an integrated circuit chip) and allow the chip to be electrically connected to external circuitry. The chip typically has a surface containing active circuit elements that can be accessed via conductors on the chip, such as bonding pads. The chip can be packaged using numerous packaging techniques, as is known in the art. The package can then be placed into a printed circuit board (PCB) to access the circuitry on the IC chip and perform desired operations. External leads, such as bond fingers, exposed through the package allow electrical input/output connections between the enclosed chip and the PCB.
As the complexity of operations and applications increases, a greater number of inputs to and outputs from the chip may be needed to implement the necessary functions. However, this typically requires increasing the size of the package. The increased complexity also results in a greater number of chips needed on the PCB to implement the necessary functions Further, with the increased complexity comes a need for a greater number of chips on the PCB to implement the necessary functions. Conventional methods to increase the number of chips without increasing the package size is to stack multiple chips on the package, in which typically two or more stacked die are each electrically connected to leads on the package or lead frame. However, a faulty die on the package can consume one or more good die, thereby reducing yield.
Thus, it is desirable to have a die package without the disadvantages discussed above associated with conventional packages.
In the present invention, a method and structure utilize exposed internal leads to provide additional input/output connections or additional die to be stacked and connected.
According to the one embodiment of the present invention, electrically isolated signal traces within the paddle area are created for die signal connection and held together using lead lock tape. These signal traces or internal leads are completely internal to the package and not connected to the external leads. The internal leads are down set or bent during the lead frame manufacturing process before the die assembly process. After a die is attached to the package, bond wires are connected from the die to both the external and internal leads. The die and bond wires are then. encapsulated, with the ends of the internal leads exposed. The die contained in the resulting package can then be connected to external circuitry, such as a printed circuit board, through both the external and internal leads. In addition to the external and internal leads, an exposed die pad to the internal leads can also be used to connect the die to the printed circuit board. Consequently, an increased number of inputs to and outputs from the die is available.
In another embodiment, the internal leads are down set or bent away from the ends of the external leads. After wire bonding and die encapsulation, the ends of the internal leads are exposed on an upper portion of the die package. A second die package can then be stacked onto this first die package, with external leads from the second die package electrically coupled to the internal leads from the first die package. This allows electrical connection between the two dies in a smaller profile package.
In one set of embodiments, the internal leads and external leads are not interleaved, i.e., the ends of the leads to not overlap. This allows a smaller exposed area of the internal leads. In another set of embodiments, the internal leads and external leads are interleaved, i.e., the ends of the internal leads extend beyond the ends of the external leads. These embodiments allow shorter bond wires to be used for connecting the die to the external leads.
The present invention will be more fully understood when taken in light of the following detailed description taken together with the accompanying drawings.